The present invention relates to a distance measuring apparatus which scans a laser beam in one direction and receives the light beam reflected from an object in the direction to calculate the distance to the object on the basis of the received light signal.
As one example of such kinds of distance measuring apparatus Examined Japanese Patent Publication No. Sho. 55-1555 proposes an apparatus which confines laser light emitted from one light source in a horizontal direction by an optical system to make an elliptical or rectangular laser beam enlarged in a vertical direction and scans the resultant laser beam in the horizontal direction at a fixed period to measure the distance to an object in the beam direction for each scanning angle.
Examined Japanese Patent Publication No. Sho. 61-54187 proposes an apparatus which raster-scans a field of view with a laser beam by an X - Y scanner to measure a distance two-dimensionally.
Where distance measuring is to be performed in plural directions by scanning in such a distance measuring device, in order to complete the distance measuring in all desired directions, it is necessary to perform the one-direction distance measuring by the number of times corresponding to the number of divisions. Generally, the projection of a laser beam by one light source requires a relatively long period because of several electrical limitations. It takes time to perform the projection a large number of times, i.e. distance measuring. Actually, the scanning mechanism for directing the beam to a predetermined direction must be driven by the number of times corresponding to the above number of divisions. Thus, it takes a considerably long time to complete the distance measurement in all directions.
Such a kind of distance measuring apparatus is mounted in a vehicle e.g. toward its running direction to detect simultaneously plural preceding vehicles and/or obstacles on a road thereby recognizing these preceding vehicles or generating a warning of the obstacles. In this case, since the vehicle at issue and preceding vehicles are always running, if it takes a long time for distance measurement, the objects (precedent vehicles, obstacles, etc.) in the field of view ahead of the vehicle at issue will shift greatly during the distance measurement. As a result, detection of the distances to the objects and time-change in scanning directions will be delayed. This leads to a recognition delay for the vehicles and obstacles or false recognition producing a false warning. Accordingly, there is a possibility that the above apparatus cannot be actually used.